<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<script src="https://cdn.bootcdn.net/ajax/libs/marked/1.2.7/marked.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>

<style>
    html,body,#app{
        margin: 0;
        height: 100%;
        color: #555;
    }
    textarea,#app div{
        display: inline-block;
        width: 48%;
        height: 100%;
        vertical-align: top;
        box-sizing: border-box;
        padding: 0 20px;
    }
    textarea{
        border: 0;
        border-right: 2px solid #888;
        outline: 0;
        background: #d8d2d2;
        padding: 20px;
        background-image: url(./img/111.png);
        background-repeat: no-repeat;
        background-size: 50%;
        background-position: 60% 60%;
    }
</style>



<body>



<div id="app">
    <textarea v-model="val"></textarea>
    <div v-html="mark"></div>
</div>


    <script>
        let vm = new Vue({
            el: "#app",
            data: {
                val: "# HELLO"
            },
            computed: {
                mark() {
                  
                    return marked(this.val)
                }
            }
        })
    </script>
</body>

</html>